Process for the melting, refining, and casting of magnesium and its alloys



Patented H Aug. 31, 1937 UNITED STATES "PATENT OFFICE PROCESS FOR THE MELTING, REFINING, AND CASTING OF MAGNESIUM AND ITS ALLOYS Alfred Claude Jessup, Clamart, France, assig'nor to Societe de Produits Chemiques des Tel-res Rares, Paris, France 'No Drawing. Application December 2, 1936, Se-

rial No. 113,933. 1995 I 5 Claims.

even when the temperature of the metal does not I greatly exceed its melting point.

It has therefore been constant practice to melt, refine, and cast magnesium and its alloys under a protective covering which prevents attack of the metal by air. This may be done either by the use of inert gases in a completely enclosed l5 crucible, or in the case of open crucibles by means of certain fluxes which form a-fllm between the metal and the atmosphere. It has also been proposed to, decrease the inflammability of magnesium and its alloys by incorporating'from A cast without other protective means. The addi- A very 'large number of salts and mixtures of salts have heretofore been proposed to enable the metal to be melted, reflned and cast out of contact with air. Most of these consist, at least in part, of halogen salts of magnesium, the alkali and the alkaline earth metals. Some of these mixtures having a low melting point are in fact capable of greatly diminishing the attack of the metal during melting, and are also capable of absorbing to a large degree the impurities which it is desiredto remove from the metal when it is refined. Ithas however been found that even when using the best of these fluxes, castings are produced which include a considerable amount 01 the flux, unless the stirringof the metal is followed by a settling step lasting at least 10 minutes. These foreign particles act in a highly corrosive and therefore deleterious manner. The use of such fluxes is therefore impossible 'in diecasting, where several castings have to be made a minute.

The present invention consists in a process for 5 the melting, refining and casting of magnesium and its alloys, in which attack of the molten metal by air is almost completely obviated, and

corrosive inclusions entirely excluded. According to the invention this result is achieved by the 55 use Jf a flux consisting principally of a substanto 5% of Ca, in which case the metal can be- In Germany December 19,

tially eutectic mixture of the fluoride and chloride of calcium or strontium together with barium fluoride."

The efficient action of such a salt mixture is all the more surprising in as much as it is known that a flux consisting of aeutectic mixture of calcium chloride and :calcium fluoride (82% CaClz 18% CaFz) is inappropriate. It could therefore in no way have been foreseen that satisfactory is cast from a pot at the rate of several pours a minute, as is the case in die-casting. The cause of this factappears to lie in the high surface tension of the flux in question, which permits the flux spreading out in a thin protective film over the surface of the molten metal, while at the same time preventing it penetrating the surface of the metal and so finding its way into the interior of the melt. For the same reason the fllm of flux is not inclined to follow the metal when this is poured from the pot, Should however a little flux follow the metal, this always remains on the surface,.never in the interior, and can thus be removed by pickling in acid.

The composition of the aforesaid fluxes can vary within somewhat wide limits. hand mixtures on both sides of the eutectic mixture can be employed; and onthe other, both calcium chloride and calcium fluoride can be partially or entirely replaced with strontium chloride or fluoride. Too large quantities of barium fluoride should be avoided, as this salt serves rather to reduce the protection the film affords against the air. But within certain limits, the proportions of barium fluoride can also be varied. A few per cent can be employed, but preferably the proportion isxmaintained somewhat higher. A flux whose composition is particularly well adapted to die-casting has the following composition:

Per cent CaClz 60 CaFa 15 BaFz -L 25 On the one Simultaneously, or after adding the flux, one can,

in known manner, sprinkle sulphur over the ladles .contents.

The more finely powdered and intimately mixed is the. flux, the more eflicient is its action.

Having now particularly described and ascertained the nature of my invention and in what manner the same is to be performed, I declare that what I claim is:

1. Process for the melting, refining and casting or magnesium and its alloys, which comprises treating the metal with a flux consisting primarily of the chloride of a metal of the group constituted by calcium and strontium and the fluoride accused barium fluoride.

2. Process according to claim 1, in which the proportions of the chloride and the fluoride of the metals of the group constituted by calcium and strontium, are substantially those existingv in one of the eutectic mixtures which the said salts .are capable of forming amongthemselves.

3. Flux for the melting, refining and casting of magnesium and its alloys, consisting of barium fluoride, the chloride of 'a metal of the group constituted by calcium and strontium and the fluoride of a metal of the same group.

4. Flux according to claim 3, in which the proportions of the chloride and the fluoride of the metals of'the group constituted by calcium and strontium, are substantially those existing in one or the eutectic mixtures which the said salts are capable of forming among themselves.

5. Flux according to claim 3, consisting substantially of 25% barium fluoride, 60% calcium chloride and 15% calcium fluoride.

ALFRED CLAUDE JESSU'P.

of a metal of the same group, together withv 

